Television apparatus



Feb. 113, 1945. G. ZANARINI 2,359,631

TELEVISION APPARATUS Filed July 51, 1940 2 Sheets-Sheet l Patented Feb. 33, 1945 TELEVISION APPARATUS Giuseppe Zanarini, Turin, Italy; vested in the Alien Property Custodian Application July 31, 1940, Serial No. 348,856

Italy May 30, 1940 10 Claims.

This invention relates to a wireless apparatus, more particularly suited for the reception of television pictures.

The features which distinguish this apparatus chiefly concern the synchronizing circuits, video frequency amplifier and video frequency reproduction circuits; they afford a completely selfadjusting synchronization together with a perfect response of the cathode ray tube to all video frequencies concerned.

The apparatus and the functions of the various circuits shall be described with reference to the accompanying drawings, in which:

Fig. 1 shows the portion of the electric diagram of the apparatus embodying this invention and includes the video frequency amplifier, cathode ray tube and synchronizing devices.

Fig. 2 shows the diagram of the synchronizing signals;

Figure 3 shows the process of separation of the amplitude differentiated signals in the case of the signals of the type shown in Figure 2;

Figure 4 shows the wiring diagram of the hold up tube;

Figure 5 shows a diagram of a s chronizing signal of another type, by which the separator secondary emission tube may be dispensed with.

The envelope of the video and synchronizing signals, after high frequency and intermediate frequency amplification, is detected by diode V1 and then applied to the control grid of tube V: which acts, at the same time, as a video frequency and synchronizing signal amplifier. Tube V2 is of the secondary emission type, for instance of the Philips E 50 type and can therefore supply amplified signals of opposite phase, which can then be taken from the anode and secondary cathode, respectively.

The direction of the synchronizing signals was heretofore generally opposite that of the video signals so that phase reversal was necessary in order to actuate the synchronizing devices. This is no longer necessary according to this invention which uses a secondary emission tube, as the tube itself can supply the two desired signals in opposite phase. Supposing by way of example the diagram of the synchronizing signals is that given in Fig. 2, the signals for the actuation of the synchronizing devices are taken from the secondary cathode, as shown in the electric diagram of Fig. 1, while the video signals are taken from the anode and applied to the control grid of the cathode ray tube Va, after having undergone a proper correction, the particulars of which will be explained in detail hereinafter. Owing to the 25 order of 140 volts).

direct coupling existing between th rectifying diode and tube V: and between the tube V: and cathode ray tube, all shades of the image are properly reproduced.

5 The signals taken from the secondary cathode sion type (for instance EE 50 Philips type) and the main feature of the arrangement consists in a reactive coupling between the secondary cathode and screen grid. By virtue of said coupling the tube always operates (for input signals not below a certain limit, approximately 4-5 volts of the video synchronizing envelope) between a blocked condition existing during the video signals and a saturated condition existing during the interval corresponding to the syncnronizing go signals. For any value of the input signals amplitude (within certain limits) the amplitude of the separated synchronizing signals supplied by the secondary cathode of the tube V3, remains constant and of considerably high value (of the Moreover, by virtue of the reactive coupling Ce existing between the secondary cathode and screen grid, the rectangular form of the synchronizing signals is further improved, while the sensitivity to external static is de- 30 creased.

From the secondary cathode of tube V: two frequency separator circuits, respectively, are derived for the frame and line signals. Said circuits may be differently arranged according to the type of synchronizing signals. The frame signals are separated by amplitude differentiation obtained by an integration process (circuit formed by elements R53, R32, C22) The amplitude differentiated signals are then sharply discriminated by tube V4 which may be the frame signals, are of a greater magnitude than line signals and this greater magnitude of the frame signals is utilized for obtaining a sharp separation by means of tube V4. The cathode of tube V4 is made sufliciently positive to make the tube inoperative for the line signals; the frame signals only, having a greater magnitude as previously explained, can actuate the tube. Furthermore, the grid current of tube V4 operates a sharp limitation of the upper part of the frame signals (see diagram Fig. 3), causing the current of the tube to assume a trapezoidal form characterized by two sharp variations which produce in inductance L2 two voltage peaks, one of them being used to actuate tube Vs. The function of resistor R35 is to damp out of the oscillations which would follow each voltage peak.

The separation of the vertical synchronizing signals, operated by tube V4, is necessary only if the synchronizing signals are of the type indicated in Fig. 2; said separation process does not permit the line signals following the frame signals to affect the duration of the oscillation produced by the oscillator tube V5; in this case, said influence would disturb perfect interlacing, ow ing to the diiferent position of the frame signal with respect to the line signals which follow it in both cases, viz. when scanning the odd lines and even lines. 'Iube V4, for instance, would no longer be necessary if the diagram of the synchronizing signals were that of Fig. 5.

The vertical synchronizing signals, separated by tube V4, synchronize the pulse generator formed by the tube V5 also of the secondary emission type through C24. The arrangement of the circuit of tube V5 is characterized by a reactive coupling between the secondary cathode and control grid for the generation of the discharge pulses of capacity C27 which therefore generates through the charging resistor R41 saw-tooth shaped voltages synchronized with the frame signals as described in my copending U. S. application Ser. No. 340,617 filed June 14, 1940, now Patent No. 2,297,522. The operation of tube Vs thus mounted is characterized by a great flexibility in performance which owing to the considerable amplitude of the actuating signal enables a perfect and completely automatic synchronization within very wide safety limits to be obtained.

The voltage applied to resistor R41 (500 volts approximately) is stabilized by means of small neon bulbs S2, S3, S4, S5 (the current drawn is approximately 0.5 ma.) in order to avoid vertical fluctuation of the frame, caused by disturbances of a very low frequency reaching the apparatus through the supply circuit.

The saw-tooth signals generated by capacity C21 actuate through Cza the twin-pentode Vs operating in push-pull through cathode coupling. The function of the tube Va is to generate sawtooth currents which, flowing through the deflecting coil L5 generate the vertical magnetic deflection field.

As shown in Fig. l, the twin-pentode Vo has a pair of anodes, a pair of control grids and a single cathode, the latter being connected to ground through a cathode resistor and a potentiometer P4. The anodes are each connected to one end of the deflecting coil Is, the center tap of which is connected to the source of supply AnT. The saw-tooth signals from the capacity C21 are coupled through C28 to the potentiometer P3 and thence pass to ground. Connected to the adjustable tap of the potentiometer P3 is the lefthand control grid of the twin-pentode Va, the right-hand control grid of the twin-pentode Vs being connected to an adjustable tap on the potentiometer P4.

The operation of this portion of the system is as follows:

The capacity C27 is gradually charged through the resistor R41 and as the voltage across the capacity gradually increases, the voltage applied across the potentiometer P3 by the capacity C21 through the coupling condenser Can also gradually increases. As the adjustable tap of the potentiometer P3 is connected to the left-hand grid of the tube Vs, the output of the left-hand anode circuit of the twin-pentode Vs also gradually iiicreases causing the magnetic flux in the lefthand portion of the deflecting coil L4 to slowly increase thereby producing vertical deflection of the electron beam in the cathode ray tube Vs. However, as the output of the left-hand portion of the tube Vs increases, there is an increase in the current flow through the cathode resistor and the potentiometer P4 and, since the right-hand grid of the tube Va is connected to the tap on potentiometer P4, it is obvious that this grid becomes less positive with respect, to the cathode due to the increased voltage drop in the cathode resistor and the potentiometer. The right-hand side of the tube Vs therefore becomes less conductive than before with two results:

1. As the current flowing in the cathode resistor and the potentiometer P4 is comprised of the current flow through both anode circuits of the tube Vs, a reduction in the flow of the righthand anode circuit when the flow of the lefthand anode circuit is increased, and vice versa, tends to maintain the current in the cathode resistor and the potentiometer P4 substantially constant since both halves of the tube. are caused to operate in push-pull by reason of the cathode coupling between the two grids.

2. The reduction in the flow of the right-hand anode circuit when the flow of the left-hand anode circuit increases causes a reduction in the magnetic field produced by the right-hand portion of the deflectin coil Ls simultaneously with the increase in the magnetic field produced by the right-hand side of the coil and, as both halves of coil is are connected in opposition, the resultant magnetic field produced by coil L5 tends to increase linearly instead of increasing logarithmically as does the charge in the capacity C21. Compensation of the logarithmic function of the capacity occurs by reason of the fact that, while the voltage of the left-hand grid of tube Va increases logarithmically, the voltage of the righthand grid tends to decrease logarithmically due to its connection to the cathode resistor and potentiometer P4 thus producing a compensation which is the mathematical counterpart of the voltage applied to the left-hand grid and thereby eliminating the undesirable logarithmic variation in the magnetic fleld produced by coil Ls.

When a frame synchronizing impulse is received on the control grid of tube Vs, this tube discharges the capacity Car with the result that the above sequence of events repeats itself to produce a continuous vertical scanning of the oathode ray electron beam.

By the push-pull arrangement for the generation of said currents a perfectly linear deflection may be obtained with the aid of very simple means. The potentiometer Pa makes the adjustment of the amplitude deflection possible and the potentiometer P4 provides the vertical centering of the frame. Finally, said push-pull arrangement has the advantage of permitting the elimination of the coupling transformer (or impedancte) and of drawing practically constant curren Tube Vs may be for example of the Philips ELL 1 type.

The line signals taken from the secondary cathode of tube V: are separated by derivation by means of capacity C: and synchronize the pulse generator formed by the secondary emission tube be found in the portion of the potentiometer V1 (for instance of the Philips BE 50 type). Apart from the time constants which determine its natural period. said tube operates according to the invention in the same manner as the frame impulse generator formed by the tube Va and is featured by the same stability characteristics.

Capacity C12 fed by resistor R5: generates a sawtooth voltage synchronized by the line synchronized by synchronizing signals. The small neon bulb 81 operates initially only to limit the anode voltage of the tube V: while the cathode is still cold. During normal operation the tube 81 must not be glowing.

The net formed by resistor R24 and capacity Ci: gives rise to a desirable distortion of the sawtooth in order to compensate for the curvature of the mutual characteristic of the tube Vs.

The line saw-tooth signal actuates the tube Va, a high slope power pentode, for instance of the EL 6 Philips type, which generates the saw-tooth currents necessary for the generation of the horizontal deflection magnetic field.

The circuit of tube Va is characterized in that a current negative feedback is provided in order to obtain considerable deflection linearity. The adjustable resistor R29 allows adjustment of the horizontal deflection amplitude by varying the amount of feedback. The horizontal deflection coils L4 are connected to tube Vs through a proper transformer T1. The damping net RaoCic renders the deflecting circuit aperiodic in order to avoid parasitic oscillations.

Horizontal centering of the frame is obtained by supplying the deflecting circuit with a proper amount of D. C. by means of the center-tapped potentiometer P1.

The coils In provide the magnetic concentration of the cathode beam and focussing of the picture is obtained by adjusting the value of the variable resistor R31. The anode and cathode of the oathode ray tube, according to the invention, are in a special potentiometer circuit including elements Res, R40, R50, R51, P2 and 11. The capacities C20, C21 and C19 have a smoothing action.

Said potentiometer circuit is featured by the presence of a point M in which the voltage with respect to ground is independent of the current consumption of the cathode ray tube. Said voltage may be chosen within certain limits by properly designing the potentiometer elements and, according to the invention, the same voltage is used to feed the discharge devices which generate the saw-tooth line and frame signals needed for driving tubes Va and V6, respectively.

As will be seen in Fig. 1, the anode of the cathode ray tube V9 is connected to a point between the resistors Rra and R40, of the potentiometer circuit, which is energized from the high voltage source AiT. The cathode of tube Va is connected to a point on the potentiometer circuit between the resistor R51 and neon tube So. the function of which will be described hereinafter. It is obvious, therefore, that the cathode-anode circuit of the cathode ray tube V9 is connected in parallel with the neon tubes Se, S7 and the resistors R50 and R49 and that any variation in the current consumption of the cathode ray tube due to the variations in the signal placed on its control grid will cause variations in the voltage drop across elements Sc, 81, R50 and R49. However, if the resistances of the resistors Ra, R0 and Ru are made equal, and the resistance of the neon tubes Sc and S1 added to that of the resistor R60 is made equal to the resistance of each of resistors Rn, Ru and R51, a point such as M will comprised of elements 8a, 57, R50 and R40 which is electrically in the center thereof and in which no voltage variation with respect to ground takes place regardless of the variations in the voltage across said portion of the potentiometer when the load on the cathode ray tube varies. In these respects, the potentiometer is structurally similar to and acts like a bridge. The point M, because it holds a constant voltage is connected to charge the frame capacity C27 through the resistor Ru and the line capacity C1: through the resistor Rs: to thereby produce uniform sawtooth deflecting voltages for the scanning operation of the cathode ray beam.

The voltage of the point M may be chosen of a considerably high value (for instance, 1000 volt with Ait=-5000 volt) in order to obtain saw-tooth voltages of a very linear form and of considerable amplitude (as required, for instance, for the actuation of tube Vs owing to the feedback arrangement of the same). The resistor R51 which is an element of the potentiometer circuit, is properly designed in order to safeguard the cathode ray tube, should the Art voltage (about 300 volt) accidentally fall.

In such case, the control grid of tube Vs would fall to ground potential, while the cathode of the tube would assume with respect to ground the voltage appearing across R51, said voltage being chosen of a value sufllcient to cause blocking of the tube. The current of the electronic beam of tube Va flowing in resistor R51 produces a negative feedback effect, its value depending upon the frequency in relation with capacity C18.

The lower the frequency, the greater the negative feedback will be and, according to the invention, it is totally compensated for by means of the net ReCa placed in the anode circuit of the video frequency amplifier tube Va. The effect of the net RoC: consists in an increase in the amplification of the lower frequencies and is such as to' exactly compensate for the negative feedback just described.

The cause of the negative feedback will readily become apparent from a study of Fig. 1. The cathode of the cathode ray tube V9 is connected to ground through resistor Rm, potentiometer P: and the thermic delayed relay 11. As the control grid circuit of the cathode ray tube is connected to ground through the amplifier V2, the cathode. current of the cathode ray tube, as it flows through resistor R51, will cause the groundedend of resistor R51 to become more negative and thus place a negative bias on the grid of the cathode ray tube. This bias will vary in proportion to the feedback current through the resistor Ru which 1 is in turn responsive to the frequency of the video signals applied to the cathode ray tube Va. Because of the presence of capacity Cia, a lowfrequency will cause more feedback than a high frequency and this variation produces an error in the video reception which requires compensation by means of the network R; in the mannerpointed out hereinabove.

The two small neon bulbs Sc and S1 stabilize the potential diiference existing between the screen grid and cathode of the cathode ray tube Vs. Said stabilization is very useful, considering that the screen grid current of the cathode ray tube of the same type may assume widely different values. Potentiometer P2 allows adjustment of the average bias of the cathode ray tube and consequently varies the medium shade of the picture. The thermic delayed relay I1 avoids the Y iormation oi the luminou spot on the fluorescent screen at the time when the set is switched on and the cathodes or the tubes are still cold.

The external controls of the assembly just described are reduced to a single control P: for the adjustment of the medium shade. All other semifixed elements (R2, R29, R31, P1, P3, P4) are inside the apparatus and are adjusted during the lining up of the set.

No control is Provided for the adjustment of synchronization, as thisis completely self-adjusting. Practically, it was found unnecessary to provide the set with controls of that kind owing to the wide safety limits of the synchronizing circuit.

What I claim is:

1. In a television apparatus a push-pull circuit for magnetic defiexion of cathode rays comprising in combination with a cathode ray tube a twinpentode having a cathode coupling consisting of a single set of cathode resistors, deflectin coils 5. In a television apparatus, a cathode ray tube 5 having a control grid, a cathode, an anode, and deflecting coils, a video-frequency amplifier, a source of power supply, a potentiometer connected I tiometer, control means for said deflecting coils connected to the potentiometer intermediate said two points and at the electrical center therebetween, a connection from the output of said video- I frequency amplifier to said control grid, and

' srid.

means responsive to the output of saidvideofrequency amplifier for compensating for negative feedback between said cathode and the control 6. In a television apparatus, in combination I with a cathode ray tube having a control grid and directly connected to the anodes of said twinpentode operating in push-pull by means of said cathode coupling and means for applying a sawtooth actuating voltage to one only of the control grids of said twin-pentode.

2. In a television apparatus, a push-pull circuit for magnetic deflexion of cathode rays, comprising in combination with a cathode ray tube, a twin pentode having a cathode coupling consisting of a single set of cathode resistors, deflecting coils directly connected to the anodes of said twin pen-" tode operating in push-pull by means of said cathode and anode electrodes, a source of power supply, a video-frequency amplifier having an anode circuit, a potentiometer comprising a plu- I rality of resistors in series energized by said source of supply, cathode and anode circuits comprising connections from said electrodes to separate points on said potentiometer spaced from the ends thereof, a correcting circuit for compensating the negative feedback effect produced by the potential drop of the cathode circuit current cathode coupling, means for applyin an actuating saw-tooth voltage to one only of the control grids of said twin pentode and means for applying a constant voltage with respect to the.

cathode to one of the control grids of said twin pentode.

3. In a television apparatus, a push-pull circuit for magnetic defiexion of cathode rays, comprising in combination with a cathode ray tube, a

twin pentode having a cathode coupling consisting of a single set of cathode resistors, deflecting coils directly connected to the anodes of said twin pentode operating in push-pull by means oi. said cathode coupling, means for applying an actuating saw-tooth voltage to one only of the control grids of said twin pentode, means for applying a constant voltage with respect to the cathode to the other control grid of said twin pentode and means for adjusting the base bias oi one of said control grids of said twin pentode.

4. In a television apparatus, a push-pull circuit through one of said resistors, and a, grid circuit comprising a connection from said video-frequency amplifier anode circuit to said control grid which includes said correcting circuit.

7. Television apparatus, as claimed in claim 8, comprising an impedance placed in series in the anode circuit of the amplifier stage of the videoirequencies in turn directly connected with the grid circuit of said cathode ray tube, said impedance compensating for the negative feedback efiect produced by the impedance of the cathode circuit of said cathode ray tube.

8. Television apparatus, as claimed in claim 8,

comprising a cathode impedance of the cathode ray tube consisting of said one of said resistors and a capacitive element in parallel with each other and a compensating impedance consisting of a resistor element and a capacitive element in parallel with each other and connected in series with the anode circuit of the video-frequency amfor magnetic defiexion of cathode rays, comprising in combination with a cathode ray tube, a

twin-pentode having a cathode coupling consisting of a single set of cathode resistors, deflecting coils directly connected to the anodes of said twin plifier stage in turn directly connected with the grid circuit 01' said cathode ray tube, said impedance having the same time constant.

9. Television apparatus, as claimed in--claim 6, comprising a second potentiometer, a source of direct current connected across said second potentiometer, an adjustable slider on said second potentiometer connected to one end 01' the first potentiometer whereby a bias voltage is provided in series with said source 01 power supply for adjusting the voltage applied across said cathode and anode electrodes.

10. Television apparatus, as claimed in claim 6, comprising a screen grid in said cathode ray tube. and means included in said potentiometer for stabilizing the voltage of a portion thereof, said cathode electrode and said screen grid being connected across said portion of the potentiometer.

GIUSEPPE ZANARINI. 

